1. Normally the trips to SFO are going to be part of a 4 day trip. Some of them end with the red eye back. Occasionally you will see a SFO trip where you deadhead out and fly back or one leg to SFO with a 24 hour layover and then fly the red eye back. There are less SFO overnights during the winter since we cut back the flights during that time.
2. Pretty much any of the cities the 737 goes to can be a part of the trip.
3. If you are doing a trip that ends with a red eye it will average between 18 to 19 hours. The rest of the four days will be around 22-24 hours.